Crossed-field discharge device and means for balancing the rf anode-cathode voltages thereof



CROSSED-FIELD DISCHARGE DEVICE AND MEANS FOR BALANCING May 5, 1970 J. E. STAATS r 3,510,724

THE RF ANODE-CATHODE V OLTAGES THEREOF Filed Nov. l4, 1967 I .4 Sheets-Sheet 1 J FG. I I 8| 79 78 87 INVENTOR.

'J'AMES E- STAATS wam k x-us ATTORNEY ay 1970 J. E. STAATS 3,510,724

CRQSSED-FIELD DISCHARGE DEVICE AND MEANS FOR BALANCING THE RF ANQDE-CATHODE VOLTAGES THEREOF Filed Nov. 14, 196'? .4 Sheets-Sheet 2 JAMES E. STAATS H\S ATTORNEY 3,510,724. S FOR BALAN THEREOF .4 Sheet CING s-Sheet 4 E. STAATS DEVICE AND MEAN ATHODE VOLTAGES CROSS LONGITUDNAL.

VOLTS ENTOR.

TAATS INV JAMES E. s W/6 ms ATTORNEY United States Patent ,0

CROSSED-FIELD DISCHARGE DEVICE AND MEANS FOR BALANCING THE RF ANODE- CATHODE VOLTAGES THEREOF James E. Staats, Louisville, Ky., assignor to General Electric Company, a corporation of New York Filed Nov. 14, 1967, Ser. No. 682,753 Int. Cl. H01j 25/50 US. Cl. 31539.51 14 Claims ABSTRACT OF THE DISCLOSURE A magnetron of the type having axial propagating waves includes a first frequency determining cavity defined by the anode structure and a second frequency determining cavity defined by the end spaces and interaction space, both cavities being resonant at the same frequency. The cathode is hollow and the heater is mounted therein,

. being electrically connected to the cathode at one end and insulated from the cathode of the other to form a transmission line which is one quarter the wave length of the determined frequency. Output connections are coupled to the anode and cathode. They form a transmission line section shorted at a remote end, which is one half the wave length at the determined frequency. The end of the heater insulated from the cathode is provided with a connection forming a transmission line, shorted at its remote end. This line is one quarter the wave length at the determined frequency.

BACKGROUND OF THE INVENTION SUMMARY OF THE INVENTION An object of this invention is to provide a magnetron having an improved electronic efiiciency.

Another object of this invention is to provide such a magnetron in which the RF voltages of the cathode are balanced with respect to the anode.

A further, more specific object of this invention is to provide a magnetron of the axial propagating wave type in which the cavity defined by the anode and the cavity defined by the end spaces and interaction space are reso nant at the same frequency.

Another object of this invention is to provide such a magnetron in which the circulating current losses are minimized.

In accordance with one embodiment of the invention there is provided a crossed-field discharge device including an anode structure defining an axially extending first resonant cavity and establshing an inner axially extending space. An axially extending cathode structure is disposed in the inner space and cooperates with the anode structure to define an axially extending annular interaction space therebetween. A pair of pole plates are disposed adajacent opposite ends of the anode structure respectively to define a pair of end spaces communicating with the ends of the interaction space. The end spaces and interaction space form a second cavity resonant at the same frequency as the first resonant cavity.

3,510,724 Patented May 5, 1970 BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a partial, elevational view of a magnetron incorporating one embodiment of the present invention and showing certain connections for the magnetron, the view being partly broken away and partly in section.

FIG. 2 is a partial, enlarged vertical section of the magnetron of FIG. 1.

FIG. 3 is a fragmentary perspective view of portions of the two anode members of the magnetron, showing them in spaced apart relationship.

FIG. 4 is a fragmentary horizontal sectional view of the magnetron illustrating certain details of the anode and cathode.

FIGS. 5 and 6 are graphs plotting several operating characteristics of the device of FIGS. 1 and 2.

FIG. 7 is a graph illustrating variations of the cathode and anode vane voltages in the device of FIGS. 1 and 2.

FIG. 8 is a graph illustrating a typical field pattern in prior art devices of the general type of FIGS. 1 and 2.

FIG. 9 is a graph illustrating the field pattern of the device of FIGS. 1 and 2.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring now to FIGS. 1 and 2 there is shown a magnetron incorporating the present invention. The particular device shown is a double folded anode, crossedfield discharge device of the general type described and claimed in my copending application Ser. No. 559,267 filed June 21, 1966, and assigned to General Electric Company, assignee of the present invention. The construction of this type of device and the general mode of operation thereof are described in detail in that application.

Referring now to FIGS. 1 and 2; the magnetron or discharge device 1 generally comprises an anode structure 2 including a sleeve 3 and a pair of anode members or sections 4 and 5, a cathode structure 6, a pair of opposed end plates or pole pieces 7 and 8, an upper end structure 9 and a lower end structure 10. The anode sleeve 3 is tubular in shape, having an inner surface 11 which is cylindrical in shape and substantially circular in cross section at all points thereof, and an outer surface 12 which also is cylindrical in shape. The inner surface 11 has a recess at each end which defines an upper end wall 13 and a lower end wall 14.

Mounted on the sleeve 3, at substantially the mid point thereof and extending outwardly therefrom is an exhaust tube 15. The tube is sealed hermetically to the sleeve and extends therethrough to communicate with the interior of the device for use in evacuating the device during manufacture. Mounted on the outer surface 12 of the sleeve 3 is a stacked array of cooling fins 16 which are secured to the sleeve 3 by some means such as brazing. The sleeve 3 and fins 16 are formed of a metal having good thermal conductivity, such as copper, for conduction of heat away from the interior of the device and radiation of the heat to the atmosphere.

The anode sections or members 4 and 5 are formed as generally inward extensions from the inner surface 11 of the sleeve 3. The construction of the anode members is shown in more detail in FIG. 3. The anode member 4 is generally annular in shape and includes a body portion 17 with an outer end wall 18 and an outer annular wall 19 sized to fit snugly against the inner wall 11 of the sleeve 3 and be connected thereto by some means such as brazing. The body portion opposite the end wall 18 is cut away or recessed to provide an inner annular wall 20 concentric with the outer wall 19 but having a substantially smaller diameter and an intermediate end wall 21, which is parallel to the end wall 18 and perpendicular to the annular walls 19 and 20. The other end of annular inner wall 20 connects with an inner end wall 22, which defines the other end of the body portion 17, the end wall 22 being disposed in a plane parallel to the end walls 18 and 21. The body portion 17 is provided with a plurality of axially extending segments 23 which project radially inwardly into the axially extending space Within the anode member for substantially the entire length of the body portion. Each of the anode segments has a rod or vane 24 extending longitudinally therefrom beyond the end wall 22.

The anode member is similarly formed, having a body portion 25 with an outer end wall 26, an outer annular wall 27 sized to fit within and be brazed to the inner surface 11 of the sleeve 3, an inner annular wall 28, an intermediate end wall 29 and an inner end wall 30. A plurality of anode segments 31 extend radially inwardly from the body portion 25 into the axially extending space within the anode member 5 and extend axially substantially completely across the body member 25. A rod or vane 32 extends axially from the inner end of each of the anode segments 31 beyond the end wall 30.

As best shown by FIGS. 2 and 3, when the anode structure is fully assembled the rods or vanes 24 each extend into one of the recesses 33 provided between the anode segments 31 and the rods or vanes 32 extend into the recesses 34 provided between the anode segments 23, with each of the rods being spaced from the adjacent segments. The anode member 4 is mounted toward the upper end of the sleeve 3 (as seen in FIG. 2) and the anode member 5 is mounted toward the lower end thereof. Further details of both the configuration and a suitable method of manufacture of such an anode structure may be had by reference to my aforementioned copending application.

When assembled, the sleeve 3 and the anode members 4 and 5 cooperate to provide an outer, axially extending space 35. The space 35 is annular in shape and is bounded on its outer circumference by the inner surface 11 of the sleeve, on its inner circumference by the inner annular walls 20 and 28 and at the upper and lower ends by the intermediate end walls 21 and 29. The anode segments 23 and 31 and the vanes 24 and 32 cooperate to form a second or inner axially extending space 36 within which is disposed the cathode structure 6. The space between the outer surface of the cathode structure and inner surfaces 37 of the anode segments and the vanes form an annular axially extending interaction space 38. Also the inner end walls 22 and 30 are spaced apart to provide therebetween a radially extending annular passage 39 which connects the outer space 35, at the midportion thereof, to the inner space 36, at the midportion thereof, and the interaction space 38 at the midportion thereof.

Referring particularly to FIGS. 2 and 4, it will be seen that the cathode structure includes a cylindrical metal wall 40 arranged with its axis disposed at the axis of the device. Mounted on the upper end of the wall 40 is a metal upper end shield 41 and on the lower end is a metal lower end shield 42. The upper end shield is mechanically and electrically connected to a cathode stud 43. The lower end shield is mounted on a hollow cylindrical ceramic insulator 44.

The cathode wall 40 is provided with a sintered porous coating 45 impregnated with a suitable electron emissive oxide material, whereby upon heating of the cathode structure 6, the coating 45 readily emits electrons from the outer surface thereof. Referring particularly to FIG. 4, it will be seen that the coating 45 is shaped to provide a plurality of outwardly extending projections 46. The number of the projections 46 is equal to the sum of the total of the combined anode segments projecting rods. For instance, if there are 15 segments and rods provided on anode member 4 and 15 segments and rods provided on anode member 5, the sum will be 30 and there will be 30 projections 46. The outer surface of the coating 45 together with the inner surfaces 37 and the segments and rods define the interaction space 38. From FIG. 2 it will be noted that the coating 45 is of a varying thickness. More particularly, it is stepped, with its greatest thickness being aligned with the ends of the anode member and its thinnest portion straddling the longitudinal center line of the device. Additional details as to the construction of the cathode structure and its mounting with respect to the anode structure may be obtained from my aforementioned copending application.

The cathode structure 6 is of the indirectly heated type and there is provided within the cathode wall 40 a heater 47, in a form of a coiled filament extending substantially the entire length of the cathode wall 40 and spaced inwardly a short distance from the inner surface thereof. The upper end of the heater 47, as viewed in FIG. 2, has an outer end or terminal 48 which is mechanically and electrically connected to the cathode stud 43 so that the upper end of the cathode and the upper end of the heater are electrcially and mechanically connected together. The lower end of the heater 47 has an outer end or terminal 49 that extends through opening 50 formed in the lower end cap 42 and is spaced from the end cap. The outer end of terminal 49 is electrically secured to the upper end of a conductor 51. The conductor 51 is formed of nickel and extends outwardly into a threaded connector 52. The connector 52 sits in an appropriate seat in the insulator 44 and has connected thereto by some suitable means such as brazing a seal member 53, which extends across the lower end of insulator 44 and then partially up its outer wall. Thus the connector 52 is securely held in position with the insulator. A metal filter lead 44a is connected to the outer, threaded end of the connector 52.

The upper and lower pole pieces 7 and 8 are mounted within the outer ends of the anode sleeve 3 and form and plates for the device 1. The pole pieces are formed of a material such as low carbon steel having high magnetic permeability and are copper plated to render the outer surfaces thereof highly conducted to RF energy. Each of the pole pieces 7 and 8 is generally cylindrical in shape and includes a first substantially fiat pole plate, 54 and 55 respectively, which are disposed in a plane substantially normal to the longitudinal axis of the device and in alignment with the interaction space 38 and the anode members 4 and 5. Each of the plates 54 and 55 are spaced a predetermined distance from the adjacent ends of the anode members to form end spaces of predetermined size, 56 and 57 respectively. Each of the pole pieces includes an outwardly turned annular flange, 58 and 59 respectively, which is received in the recessed portions of the sleeve 3 forming the upper and lower end walls 13 and 14, with the end walls supporting the corresponding pole piece. The bend in the pole pieces between the pole plate and the flange is positioned to be received in the corresponding recessed portion of the sleeve 3 so that the pole plates 54 and 55 are substantially flat over their entire surface radially inward of the sleeve 3. The flanges 58 and 59 are hermetically sealed to the adjacent portions of the sleeve 3 during the manufacturing process to provide a seal in those areas. End plate 54 is provided with a central opening 59 generally in alignment with the upper end of the cathode structure 6 and end plate 55 is provided with a similar central opening 60 in alignment with the lower end of the cathode structure. These openings receive the upper and lower terminals of the cathode structure and heater therethrough.

The upper end structure 9 and the lower end structure 10 serve to provide a hermetic seal between the associated pole pieces 7 and 8 and the associated connections to cathode structure and/or the heater, as the case may be. The upper end structure 9 includes a short tube 61 having its lower end disposed in the openings 59 and hermetically secured to pole plate 54 as by brazing. The tube extends upwardly from the pole plate 54 substantially concentrically with the longitudinal axis of the device and the axis of the cathode stud 43. The upper end of the tube 61 receives the lower end of an annular insulator 62. A ring 63 fits within a recess in the lower end of the insulator 62 and about the periphery of the cathode stud 43 to provide support therebetween. A cap 64 surrounds the upper end of the insulator 62 and the adjacent portion of the cathode stud 43 and is hermetically sealed to both as by brazing. The tube 61 and cap 64 are both formed of a material that can be readily secured both to a metal and to a ceramic surface, one such material being Fernico alloy, a typical composition being 54% iron, 28% nickel and 18% cobalt. It will be seen that the upper end structure 9 provides a good hermetic seal and also provides electrical insulation between the upper pole piece 7 and the output conductor in the form of cathode stud 43. The end structure also provides the necessary mechanical support for the cathode structure 6 to position it within the anode structure 2.

The lower end structure includes the annular ceramic insulator 44, which has an outer diameter just slightly less than the diameter of the opening 60 in the lower pole plate 55 and an inner diameter just slightly greater than the outer diameter of the portion of the lower end shield 42 forming the opening 50. The lower end shield 42 is supported on the upper end of the insulator 44 with the flange forming opening 50' being received within the inner opening of the inslator, whereby the insulator serves to center and support the lower end of the cathode structure with respect to the lower pole piece 8 and particularly the lower pole plate 55.

The insulator 44 extends outwardly well beyond the pole plate 55 and is provided with a seal member 65 which is annular in shape and surrounds the insulator 44. The seal member includes a mounting flange 66 which is secured to the outer surface of pole plate 55 by some suitable means such as brazing. The seal member also includes an outer flange 67 which surrounds, engages and is secured to the outer surface of insulator 44. The seal member 65 is made of the same material as the sleeve 61 and cap 64 and is hermetically sealed both to the end plate 55 and the insulator 44. The outer end of the insulator 44 carries thereon the second seal 53, which includes an annular flange 68 surrounding the outer end of the insulator 44 and sealed thereto and a radial flange 69 which extends inwardly between the end of the insulator 44 and the adjacent end of (filter lead 44a. The seal 53 is formed of the same material as the seal 65 and is hermetically sealed both to the insulator 44 and to the lead 44a. The lower end structure 10 therefore hermetically seals the lower end of the device 1 and also provides insulation between the lower end of the cathode structure 6, associated pole piece 8 and the heater 47, all the while providing for the mechanical support of the lower end of the cathode structure 6 and the lower end of the heater 47.

Additional details of a configuration and a suitable mode of manufacture for the end structures and their attachment to the remaining portions of the device may be had by reference to my aforementioned copending application.

When the device 1 is incorporated as a crossed-field discharge device in a microwave circuit, the pole pieces 7 and 8 are utilized for establishing a unidirectional magnetic field extending axially through the several spaces within the sleeve 3, and specifically through the outer axially extending space 35, the inner axially extending space 36, the interaction space 3 8, the annular radially extending passage 39 and the end spaces 56 and 57. To this end a pair of magnetic coils 70- and 71 have been provided with the coil 70 being disposed about the upper end of the device, as viewed in FIG. 1, and the coil 71 being disposed about the lower end of the device, as viewed in FIG. 1. The magnetic coils 70 and 71 are each formed as a toroid wound of electrically conductive wire and dis posed about magnetic cores 72 and 73 respectively. The cores are each in the form of a cylinder disposed within the opening in the associated coil. There is further pro- 6 vided an outwardly extending flange 74 over the top of coil 70 and a similar flange 75 under the coil 71. A suitable casing 75a is secured between the coil 70 and flange 74 at one end between the coil 71 and flange 75 at the other end and form both a mechanical connection and a good magnetic path therebetween. It will be understood that the pole pieces 7 and 8, the magnetic cores 72 and 73, the flanges 74 and 75, and the casing 75a are all formed of metal having a high magnetic permeability, such as soft iron or low carbon steel; whereby when the mag netic coils 70 and 71 are energized, a strong and uniform unidirectional magnetic field is established between the pole pieces 7 and 8 extending axially through the spaces within the device. In order to assure a good RF con nection between the cores 72 and 73 and the adjacent pole pieces 7 and 8, suitable RF gaskets 72a and 73a are provided between the radially outer corner of the cores 72 and 73 and the adjacent pole piece 7 and 8 respectively,

Referring particularly to FIG. 1 of the drawings, there will be described desirable means for forming certain connections for the crossed-field discharge device. An electrically conductive outer bullet 76 is mounted on the interior surface of the magnetic core 72 and extends upwardly therethrough, the core 72 serving to connect it to the anode structure. The upper end of the outer bullet is received in the depending end 77 of a tubular conductor 78 which is formed of a material that is electrically conductive. The tubular conductor 78 is T-shaped, including a depending tubular leg portion 77 and a pair of oppositely extending arm portions 79 and '80, which are also tubular in configuration. A tubular electrical conductor 81 is received in the end of arm portion 79 and is mechanically and electrically connected thereto to form an extension of the arm 79. A second tubular conductor 82 is received within the first tubular conductor 81 and the arm portion 79 but is separated therefrom by a sleeve '83 of electrically insulating dielectric material, the sleeve 83 preferably being formed of a synthetic organic plastic resin, the preferred resin being tetrafiuoroethylene resin sold under the trademark Teflon. The insulating sleeve provides isolation for DC. and 60 cycle electric energy but passes RF electrical energy.

The cathode terminal 43 is mechanically and electrically joined to an electrically conductive inner bullet 84. The inner bullet extends upwardly through the outer bullet into the T-shape tubular conductor. The inner bullet is mechanically positioned by means of a suitable insulative washer 85 which closely surrounds the inner bullet and is held in position by engagement with the upper end of the outer bullet 7'6 and an appropriate ledge formed in the depending leg portion 77 of the tubular connector 78. At its upper end, the inner bullet is mechanically and electrically joined to an inner conductor 86 which extends through the conductors 81 and 82 and the arm 79 to form therewith a coaxial transmission line. The inner conductor 86 also extends through the arm and the coupler 87 connected to the end thereof. The arm 80' and coupler 87 together with the inner conductor 86 form appropriate connections for connecting the discharge device 1 to a suitable load which it is desired to energize from the discharge device.

The end of tubular conductor 82 is provided with a transverse section 88 extending substantially completely across the end of conductor 82 and a conductive screw or stud 89 which is threadedly received in the end of the inner conductor 86 engages transverse section 88 to mechanically and electrically connect the inner and outer conductors at this point. Thus this end point is provided with a short circuit or a very low potential point. The inner conductor 86 is formed with both large diameter sections such as those shown at 90, and small diameter sections such as that shown at 91 thereby to provide capacitive and inductive sections in the coaxial transmission line, as is well known in the art. By appropriate sizing of these various sections I provide the transmission line from transverse section 88 to the juncture 92 of the conductor 86 and the inner bullet 85 with an effective electrical length of one quarter wave length at the operating frequency of the device 1. The portion of the transmission line from the juncture 92 to the junction 93 of the cathode stud 43 and the upper end shield 41 is also designed to have an effective electrical length of one quarter wave length at the operating frequency of the device 1. This is done by controlling the relative size of the cathode stud 43 and the inner bullet 84 in relationship to the outer bullet 76 and the leg portion 77 of the conductor 78. These two transmission line sections form a transmission line which is effectively one half wave length at the operating frequency of the device and cause the area of the junction 93 to tend to be a low impedance point, regardless of the load connected through the coupler 87.

At the lower end of the device, as seen in FIG. 1, a filter cup 94 is received within the magnetic core 73 and spaced from the filter lead 44a. The filter cup 94 is physically separated from the magnetic core 73 by an insulating sleeve 95 which fits therebetween. The sleeve 95 is made of an electrically insulating dielectric material such as the synthetic organic plastic resin tetrafiuoroethylene to provide isolation between the magnetic core and the filter cup for DC. and 60 cycle electrical power but to readily pass RF electrical energy. The lower end of the cup 94 is formed with a transverse section 96 extending substantially completely across the end of the cup and a conductive stud or screw 97 is threadedly received in the lower end of the filter lead and engages the transverse section 96 to hold the section 96 into firm electrical contact with the filter lead 44a. This provides a heater connection which forms a coaxial transmission line. By appropriate sizing of the elements this line is caused to have an effective length from its end 96 to the lower end cap 42 which is one quarter wave length at the operating frequency of the device. Since the end 96 is a low resistance point, the one quarter wave length section will tend to cause a high resistance between the end cap 42 and the adjacent pole plate 55.

Viewing FIG. 2, it will be seen that the cathode structure 6 and heater 48 form a coaxial transmission line within the cathode structure, which is provided with a low resistance at the end cap 41 and is open ended at the end cap 42. The spacing between the cylindrical metal wall 40 and the helically coiled heater 47 is sized so that this coaxial transmission line has an effective electrical length of one quarter wave length at the operating frequency of the device. Thus the internal structure of the cathode and heater is properly designed to cooperate with the external connections of the device to provide for maximum output and minimum internal heating of the device caused by RF circulating currents.

Referring now to FIGS. 2 and 3, it will be seen that during operation of the crossed-field discharge device 1 the anode sleeve 3 together with the anode members 4 and 5 provide a folded coaxial transmission line within the device 1. This coaxial transmission line is formed to accommodate axially extending RF waves therein and provide a frequency determining folded resonant cavity for the device. More specifically the coaxial transmission line includes an outer coaxial transmission line generally corresponding to the space 35. The portion of the outer surface 11 between intermediate end walls 21 and 29 provides the outer conductor and the inner walls 20 and 28 provide the inner conductors for this outer coaxial transmission line, with this outer line being shorted at the upper end by the wall 21 and the lower end by the wall 29.

The anode segments 23 on the upper anode member 4 and the rods .or vanes 32 on the lower anode member 5 cooperate to provide a first portion of an inner coaxial transmission line for accommodating an axially extending RF wave therein. The upper end of this inner coaxial transmission line is open and the lower end connects through radial passage 39 with the midpoint of the outer transmission line. In a like manner the anode segments 31 of anode member 5 and the rods or vanes 24 of anode member 4 cooperate to provide a second portion of the innner coaxial transmission line for accommodating an axially extending RF wave therein. The lower end of the second portion of the inner coaxial transmission line is open and the upper end is connected through radial passage 39 to the midpoint outer coaxial line formed in space 35.

In operation of the device 1, the upper portion of the outer transmission line 35, that is the portion between end wall 21 and the radial passage 39 cooperates with the first or upper section of the inner transmission line to provide a resonant cavity which can be excited to cause oscillations therein at a frequency having a Wave length equal substantially to four times the length thereof, i.e., four times the distance from the end wall 21 down through the space 35, out through the passage 39 and upwardly along the vanes '32 and segments 23 to the upper ends thereof, whereby there is provided an axially extending wave therein which is reflected by the end wall 21 at one end and by the open end of the transmission line at the other end to produce a standing RF wave. The lower portion of the outer transmission line of end space 35, i.e., the portion between the end wall 29 and the radial passage 39 cooperates with the second or lower portion of the inner transmission line to provide a resonant cavity which can be excited to cause oscillation therein at a frequency having a wave length equal substantially to four times the length thereof. The two transmission lines thus described actually cooperate in the operation of the device. More specifically, when an axial RF wave is excited in the inner transmission line this RF Wave is transmitted to the outer transmission line through the passage 39 and becomes reflected by the end walls 21 and 29. The reflected wave travels back through the space 35, inwardly through the passage 39 and then flows toward each end of the inner transmission line. When the RF wave reaches the open circuited ends of the inner transmission line, reflection again occurs and a standing wave is provided. Thus the device 1 includes a double folded resonant cavity equivalent to a one half wave resonator disposed in generally a one quarter wave length space.

In order to operate the device 1 as a crossed-field discharge device a predetermined pattern of electrical magnetic fields must be produced within the device. The operating potentials for the device may be derived from a suitable power source such as that described in my aforementioned copending application. The provision of 3+ and B- potentials to the outer anode sleeve 3 and the cathode structure 6 respectively will provide a unidirectional electric field that extends between the anode segments and vanes on the one side and the cathode projections on the other side. The lines of this field are transverse to the longitudinal axis of the device and are shown schematically in FIG. 11 of the aforementioned application and are described in more detail therein.

In order to provide the necessary unidirectional magnetic field normal to or crossed with respect to the electrical field, a DC. current is established in the magnetic coils and 71. This causes a strong unidirectional magnetic flux to be established in the spaces provided within the anode sleeve 3, the path of said flux being substantially parallel to the longitudinal axis of the device. This field is illustrated schematically in FIG. 12 of my copending application and is described in more detail therein.

The coaxial transmission line formed by the double folded cavity, as described above, forms a tuned or frequency determining cavity which is readily excited at a frequency having a wave length corresponding to four times the distance from the end wall 21 down through the cavity 35, outwardly through the passage 39 then upwardly between the segments 23 and rods 32 to the outer end wall 18. When this tuned resonant cavity is excited by the establishment of the aforementioned unidirectional electrical field and unidirectional magnetic field, the cavity resonates at a frequency having the wave length mentioned, i.e., a standing RF wave is established within the tuned cavity and extends axially thereof and axially of the device 1 and through the outer space 35 and the interaction space 38. The wave length of the RF wave thus generated is actually substantially greater than four times the distance from inner end wall 21 down through space 35, out through passage 39 upwardly between the segments 23 and rods 32 to the end wall 18 because of the high capacitance between the anode segments and the rods, which high capacitance is in the tuned circuit and serves to permit the generation of RF waves in the device having wave lengths substantially greater than four times the physical distance.

There is believed to be associated with the standing RF wave thus established, an RF electrical field disposed normal to the axis of the device 1. At any moment the anode segments 23 will have one RF polarity while the rods 32 have the opposite RF polarity, whereby there is a relatively strong RF electrical field between the anode member 4 and the rods or vane 32 as well as a relatively weak RF electrical field between the anode member 4 and the cathode structure 6 and between the rods 32 and the cathode structure 6. The anode sleeve 3 also has an RF polarity opposite to that of the anode member 4 whereby there is an RF electrical field therebetween, through the space 35. Similar instantaneous RF electrical fields are formed with regard to anode member 5. These fields are diagrammatically illustrated in FIG. 13 of my copending application and described in more detail therein.

Associated with the RF electrical fields of the standing RF wave is an RF magnetic field which is believed to include circumferential flux lines passing through the cavity 35 and the interaction space 38 as well as additional magnetic flux lines formed circumferentially around the various rods or vanes 24 and 32. This magnetic field is diagrammatically illustrated in FIG. 14 of my copending application and described in more detail therein. Both the RF electrical field and the RF magnetic field associated with the standing RF wave are disposed transverse to the longitudinal axis of the device. These fields extend into the interaction space 38 and couple the cathode structure 6 to the anode structure 2. Upon the application of the operating potentials to the device and upon the cathode structure 6 being heated to the operating temperature thereof by the heater 47, electrons are emitted from the emissive coating 45 into the interaction space 38, where they are subjected to the action of the unidirectional fields and the RF fields described hereinabove. These fields cause the electrons to follow spiral paths and eventually the spiral paths of the electrons carry them into contact with the anode members thereby to complete an electrical circuit through the device 1. During the time that the electrons are in their spiral paths they impart a portion of their energy content to the RF standing wave within the device and add power thereto and reinforce the RF standing wave. A more detailed description of the interaction of the various fields of the device may be hadv by reference to my copending application.

The composite fields in the device couple the cathode structure 6 to the RF standing wave within the interaction space 38 so that the cathode structure may be used as a probe forremoval of a portion of the RF energy from the tuned cavity for supply thereof to the coupler 87.

The efficiency of prior art devices has been limited because the RF voltage of the cathode structure has been inherently unbalanced relative to the RF voltages on the anode vanes and segments. Since, as stated above, the various electric and magnetic fields present in the interaction space 38 couple the cathode structure to the standing RF wave provided in the resonant cavity defined by the anode structure the efficiency has been limited by this unbalance between the cathode and the anode.

As an important aspect of this invention I provide means for insuring that the RF voltage on the cathode is balanced with respect to the RF voltage on the vanes and segments. The end spaces 56 and 57 in conjunction with the interaction space 38 define a second resonant cavity. The end spaces 56 and 57 are sized to be inductive in nature while the interaction space is sized to be capacitive in nature. As an important aspect of this invention I space the end walls or pole plates 54 and 55 from the axial ends of the anode members 4 and 5 and from the ends of the cathode structure 6 a predetermined distance and control the distance between the outer edge of the coating 45 and the inner surfaces 37 of the segments and rods so that this second resonant or frequency determining cavity is resonant at the same frequency as the resonant cavity defined by the anode structure. This second resonant cavity defined by the ends spaces and interaction space is designed to have an effective length which is one half the wave length of the frequency determined by the first or anode resonant cavity. Even more particularly, the end space 56 and that portion of the interaction space from end wall 18 to radial passage 39 forms a first coaxial transmission line which has an effective length of one quarter the wave length of the determined frequency while the end space 57 and that portion of interaction space 38 between the end wall 26 and the radial passage 39 forms a second coaxial transmission line having an effective length of one quarter the wave length of the determined frequency. These two transmission lines are coupled at their common end to form a single resonant cavity having an effective length of one half the wave length of the determined frequency. The common resonance between the two frequency determining resonant cavities within the device 1 insures that the RF voltage of the cathode structure is balanced relative to the RF voltages on the anode segments and vanes.

' This balanced condition is illustrated in FIG. 7 wherein the numbers 1 and 2 indicate alternate sets of vanes or segments. The letter C indicates the cathode structure and the solid and dash lines indicate positive and negative RF voltages at different times in the RF cycle. It will be seen from FIG. 7 that the voltage between the cathode and the vanes and segments is uniform along the longitudinal axis of the device.

FIGS. 8 and 9 illustrate in a slightly different manner the phenomenon illustrated by FIG. 7. FIG. 8 shows the field pattern in a prior art device wherein the pattern varies between the sets of vanes while FIG. 9 shows the pattern in a device incorporating the present invention, wherein the pattern is uniform.

Prior art devices have also been limited in performance by the low circuit efiiciency due to resistive losses caused by the cavity having high circulating RF currents. As another important aspect of this invention I provide means for limiting the RF circulating currents in the cavity. This includes the common resonance of the two frequency determining resonant cavities in conjunction with the external connections for the cathode and heater and the transmission line formed by the heater and cathode. These function in conjunction to provide the low impedance area at the junction 93 and the high impedance area in the vicinity of the lower end cap 42. For instance, this high impedance area in the area of the lower end cap insures that very little of the RF energy of the operating frequency of the device flows through the heater structure 47 to cause unwanted RF heating of the device.

' There is shown in FIGS. 5 and 6 performance charts for the crossed-field discharge device 1 described above. Referring first to FIG. 5, there is shown a standard Rieke diagram superimposed upon a Smith chart, the data being obtained utilizing a series magnetic field, i.e., magnetic coils 70 and 71 were connected in series with the anode structure 2 with an applied B+ potential of 550 volts. As illustrated, a family of power curves 97 was attained, the members of the family of curves 97 for 250 watts, 300

watts, 400 watts, 500 watts, 600 watts, 700 watts, 750 watts and 800 watts being illustrated in FIG. 5. A family of curves 98 showing the frequency of operation and the frequency pulling has also been plotted in FIG. 5. FIG. 5 clearly shows that a crossed-field discharge device incorporating the present invention operates with no unstable region, as contrasted to the prior art devices which had unstable operational regions.

The performance chart for this device 1 has been plotted in FIG. 6, the applied anode voltage being plotted along the vertical axis and the anode current being plotted along the horizontal axis. In a lower portion of FIG. 6 there has been plotted a curve 99 wherein no magnetic field was provided for the device 1, whereby the values represented by the curve 99 are a measure of the emission of the cathode 6. The curve 100 is a plot with a series field connected to the device 1, i.e., the magnetic coils 71 and 72 were connected in series with the anode structure 2. There further is plotted a family of curves 101 showing the anode current for an applied anode potential when a separate magnetic field is applied to the device 1. The family of curves showing performance when the separate magnetic field has a value of 1.0, 1.5, 2.0, 2.5, 3.0, 3.5, and 4.0 amperes. There also is provided a family of curves 102, in solid lines, plotting lines of constant power output, such curves being plotted, showing values from 50 watts to 1,300 watts of output power from the device 1. Finally, there has been provided a family of curves 103, in dashed lines, plotting the lines of constant efficiency expressed in percent. Four of the curves in this family of curves have been plotted, showing values of efiiciency at 45%, 50%, 55% and 60%.

The foregoing is a description of an illustrative embodiment of the invention and it is my intention in the appended claims to cover all forms which fall within the true scope of the invention.

What I claim as new and desire to secure by Letters Patent of the United States is:

1. A crossed-field discharge device comprising:

(a) an anode structure defining an axially extending first resonant cavity and establishing an inner, axially extending space;

(b) an axially extending cathode structure disposed in said space and cooperating with said anode structure to define an axially extending, annular interaction space therebetween; and

(c) a pair of pole plates respectively disposed adjacent opposite ends of said anode structure to define a pair of end spaces communicating respectively with the opposite ends of said interaction space;

(d) said end spaces and said interaction space defining a second cavity resonant at the same frequency as said first resonant cavity.

2. A crossed-field discharge device comprising:

(a) an anode structure defining an axially extending first resonant cavity and establishing an inner, axially extending space;

(1)) an axially extending cathode structure disposed in said space and cooperating with said anode structure to define an axially extending, annular interaction space therebetween;

(c) a pair of pole plates respectively disposed adjacent opposite ends of said anode structure to define a pair of end spaces communicating respectively with the opposite ends of said interaction space;

(d) said end spaces and said interaction space defining a second cavity resonant at the same frequency as said first resonant cavtity;

(e) means for establishing an axially extending RF wave in said device, having associated therewith RF electrical and RF magnetic fields normal to the axis of said device and extending into said interaction space;

(f) output connections respectively coupled to said anode structure and said cathode structure for removing RF energy from said device utilizing said 12 cathode structure as a probe interacting with said RF fields;

(g) said second cavity being resonant at the same frequency as said first cavity insuring that the instantaneous RF potential on said cathode structure is substantially balanced with respect to the adjacent portion of said anode structure.

3. A crossed-field discharge device comprising;

(a) an anode structure defining an axially extending anode space therethrough;

(b) a plurality of axially extending anode segments on said anode structure and projecting radially into said axially extending space and providing a corresponding plurality of axially extending anode recesses therebetween;

(c) a plurality of rods respectively disposed in said anode recesses and respectively spaced from the ones of said anode segments adjacent to said anode recesses, thereby forming a frequency determining folded resonant cavity for said device;

(d) an axially extending cathode structure disposed in said axially extending sapce and cooperating with said anode structure to define an axially extending, annular interaction space therebetween;

(e) means for establishing an axially extending RF Wave in said device having associated therewith RF electrical and RF magnetic fields normal to the axis of said device and extending into said interaction space;

(f) output connections respectively coupled to said anode structure and said cathode structure for removing RF energy from said device utilizing said cathode structure as a probe interacting with said RF fields;

(g) a pair of pole plates respectively disposed adjacent opposite ends of said anode structure to define a pair of end spaces communicating respectively with the opposite ends of said interaction space;

(h) said end spaces and said interaction space defining a second cavity resonant at the same frequency as said folded cavity so that the instantaneous RF potential on the cathode structure is substantially balanced with respect to said anode segments and rods.

4. The invention as set forth in claim 3 wherein:

(a) said cathode structure is generally cylindrical in form and defines an axially extending cathode space therein;

(b) an axially extending heater structure disposed in said cathode space, said heater having one lead electrically connected to the output end of said cathode structure and its other lead electrically insulated from the other end of said cathode structure to form, with said cathode structure, a coaxial transmission line, closed at one end and open at the other, having an effective length of one quarter wave length at the frequency determined by said folded cavity.

5. A crossed-field discharge device comprising;

(a) an annular anode structure defining an outer annular axially extending space enclosed thereby, an and a radially extending passage interconnecting inner axially extending space extending therethrough said outer and said inner spaces at the longitudinal mid-section of said anode structure;

(b) said radially extending passage dividing said anode structure into a first anode section disposed adjacent to one end thereof and a second anode section disposed adjacent to the other end thereof;

(c) a plurality of axially extending anode segments on the inner surface of each of said sections projecting radially into said inner space to provide a corresponding plurality of axially extending anode recesses therebetween;

(d) a plurality of axially extending first rods on said first anode section respectively disposed in the anode recesses in said second anode section and respectively spaced from the adjacent ones of said anode segments in said second anode section;

' (e) a plurality of axially extending second rods on (f) said anode structure defining a frequency determining folded resonant cavity including said outer space and said recesses and said passage;

(g) an axially extending cathode structure disposed in said inner space and cooperating with said anode sections to define an axially extending annular interaction space;

(h) a pair of pole plates respectively disposed adjacent to the outer ends of said anode sections, each plate being spaced a predetermined distance from the corresponding anode section to define a pair of longitudinallydisposed end spaces communicating with said interaction space;

(i) said end spaces and said interaction space defining a second frequency determining resonant cavity for the device of the same frequency as said folded cavity.

6. The invention as set forth in claim 5, including:

(a) means for establishing an axially extending RF wave in said device, having associated therewith RF electrical and RF magnetic fields normal to the axis of said device and extending into said interaction space;

(b) output connections respectively coupled to said anode structure and said cathode structure for removing RF energy from said device utilizing said cathode structure as a probe interacting with said RF fields;

(c) said second cavity being resonant at the same frequency as said first cavity insuring that the instantaneous RF potential on said cathode structure is substantially balanced with respect to said anode structure.

7. The invention as set forth in claim 6 wherein:

(a) said output connections include means forming a coaxial transmission line, said line being closed at its remote end by a low impedance termination;

(b) said line being provided with an effective RF length of one half wave length at the frequency determined by said folded cavity.

8. The invention as set forth in claim 6 wherein:

(a) said cathode structure is generally cylindrical in form and defines an axially extending cathode space therein;

(b) an axially extending heater structure disposed in said cathode space, said heater having one lead electrically connected to the output end of said cathode structure and its other lead electrically insulated from the other end of said cathode structure to form, with said cathode structure, a coaxial transmission line, closed at one end and open at the other; said last named transmission line having an effective R-F length of one quarter wave length at the frequency determined by said folded cavity.

9. The invention as setforth in claim 6, wherein:

(a) said output connections include means forming a coaxial transmission line, said line being closed at its remote end by a low impedance termination for said line;

(b) said line being provided with an effective RF length of one half wave length at the frequency determined by said folded cavity;

(c) said cathode structure is generally cylindrical in form and defines an axially extending cathode space therein;

(d) an axially extending heater structure is disposed in said cathode space, said heater having one lead electrically connected to the output end of said cathode structure and its other lead electrically insulated from the other end of said cathode structure to form, with said cathode structure, a second coaxial transmission line, closed at one end and open at the other, having an effective, RF length of one quarter wave length at the frequency determined by said folded cavity;

(c) said other'terminal of said heater having connections forming a third coaxial transmission line, said third transmission line being closed at its remote end by a low impedance termination;

(f) said third transmission line being provided with an effective RF length of one quarter wave length at the frequency determined by said folded cavity.

10. The invention as set forth in claim 5, wherein:

(a)' said cathode structure physically is substantially the same length as the combined physical length of said anode sections, and is mounted substantially in register therewith;

(b) the portion of said inner and outer spaces corresponding to said first anode section and said radially extending passage defining a first folded transmission line having an effective RF length of one fourth wave length at the frequency determined by said folded cavity;

(c) the portion of said inner and outer spaces corresponding to said second anode section and said radially extending passage defining a second folded transmission line having an effective RF length of one fourth wave length at the frequency determined by said folded cavity;

(d) said end space adjacent said first anode section and the portion of said interaction space between said first anode section and the corresponding portion of said cathode structure, from that end space to said radially extending passage, form a transmission line having an effective RF length of one fourth wave length at the frequency determined by said folded cavity; and

(c) said end space adjacent said second anode section and the portion of said interaction space between said second anode section and the corresponding portion of said cathode structure, from that end space to said radially extending passage, form a transmission line having an effective RF length of one fourth wave length at the frequency determined by said folded cavity.

11. The invention is set forth in claim 10, including:

(a) means for establishing an axially extending RF wave in said device, having associated therewith RF electrical and RF magnetic fields normal to the axis of said device and extending into said interaction space;

(b) output connections respectivel coupled to said anode structure and said cathode structure for removing RF energy from said device utilizing said cathode structure as a probe interacting with said RF fields;

(0) said second cavity being resonant at the same frequency as said first cavity insuring the instantaneous RF potential on said cathode structure is substantially balanced with respect to said anode structure.

12. The invention as set forth in claim 11 wherein:

(a) said output connections include means forming a coaxial transmission line, said line being closed at its remote end by a low impedance termination;

(b) said line being provided with an effective RF length of one half wave length at the frequency determined by said folded cavity.

13. The invention as set forth in claim 11 wherein:

(a) said cathode structure is generally cylindrical in form and defines an axially extending cathode space therein;

(b) an axially extending heater structure disposed in said cathode space, said heater having one lead electrically connected to the output end of said cathode structure and its other lead electrically insulated from 15 the other end of said cathode structure to form, with said cathode structure, a coaxial transmission line, closed at one end and open at the other, said last named transmission line having an effective RF length of one quarter Wave length at the frequency determined by said folded cavity.

14. The invention as set forth in claim 11 wherein:

(a) said output connections include means forming a coaxial transmission line, said line being closed at its remote end by a low impedance termination for said line;

(b) said line being provided with an efiective RF length of one half wave length at the frequency determined by said folded cavity;

(c) said cathode structure is generally cylindrical in form and defines an axially extending cathode space therein;

((1) an axially extending heater structure is disposed in said cathode space, said heater having one lead electrically connected to the output end of said cathode structure and its other lead electrically insulated from the other end of said cathode structure to form, with said cathode structure, a second coaxial transmission line, closed at one end and open at the other, having 16 an effective RF length of one quarter wave length at the frequency determined by said folded cavity; (e) said other terminal of said heater having connections forming a third coaxial transmission line, said third transmission line being closed at its remote end by a low impedance termination; (f) said third transmission line being provided with an effective RF length of one quarter wave length at the frequency determined by said folded cavity.

References Cited UNITED STATES PATENTS 3,027,488 3/1962 WinsOr 315-3977 X 3,334,266 7/1967 Fruitiger 31539.77 X 3,255,422 6/1966 Feinstein et a1. 3l5-39.3 X 3,418,521 12/1968 Cook 31539.77 X

HERMAN KARL SAALBACH, Primary Examiner 5. CHATMON, 111., Assistant Examiner US. Cl. X.R. 

